Task: Improve the Sharpness of the Composite Video from a Commodore 64 with a Revision B Circuit Board
Needed: Commodore 64 with Revision B Circuit Board (#250407), Soldering Iron, Clippers
Time: 30-60 minutes
Introduction
The quality of the composite video from Commodore 64 bread bins is not very good. The text and graphics can be fuzzy and with color bleeding. I have previously posted about a simple mod to improve the brightness of the video from Revision A circuit boards. Here, I demonstrate how to improve the sharpness of the composite video on a Revision B circuit board (#250407) with a simple mod and with the option of soldering two wires. I learned about this mod from Adrian’s Digital Basement on YouTube. He covers the mod in detail starting around 11:30 in the video.
The simple part of the mod is to clip a single leg of two capacitors (C1 and C2) on the RF modulator board taking them out of the circuit. This improves the sharpness of the video as you can see in the comparison at the end of the post below. Optionally, you can also connect the composite signal to the RF port giving it composite out. There is also an optional conductor to bypass that might improve the signal further although I did not notice a difference.
Instructions
Before you start, be sure and record the quality of the video for comparison. Also make sure you have some metal clippers suitable for cutting through the metal legs of components on the circuit board. I have these Weller clippers I purchased on Amazon for about $20. They have been great.
First, watch the video on this mod by Adrian’s Digital Basement on YouTube. He covers the mod in detail starting around 11:30 in the video.
Second, open up the Commodore 64 by removing the top of the case and any RF shield that is on top of the board. The RF shield can be discarded.
Third, remove the metal cover of the RF modulator on the back side of the board near the RF port. I used some pliers to lift up on the tabs that hold it in place. It should pop off pretty easily. You should see the following RF modulator circuit board.
Fourth, clip one leg of each capacitor (C1 and C2) highlighted by the yellow arrows above. Feel free to complete the project at this point.
Fifth (optional), remove the green conductor highlighted by the green arrow and solder in a replacement wire. Be sure and leave enough of each leg to accept the new wire.
Sixth (optional), clip the RF wire coming up through the circuit board by the top red arrow. This removes the RF signal to the RF port. Then solder a wire to that RF connector and to the right side of the green resistor highlighted by the second red arrow.
That completes the mod. My final product is shown below along with the before and after comparison of the composite signal.
Comments
As you can see in the comparison above, the capacitor mod sharpens the video signal quite a bit. I am not sure the conductor mod does much. I could not see a difference.
There are modern solutions that will provide HDMI-quality output with special chips and boards. I will cover these later.
Thanks to Adrian Black from Adrian’s Digital Basement for the clear explanation of what to do.